IC chips are well known in the art. IC chips may contain thousands of microscopic circuit elements such as transistors, resistors, etc. Commercially-available ICs are normally contained or packaged in a molded plastic housing having a generally rectangular or square configuration, having one or more rows of evenly-spaced pins or leads extending perpendicularly from one face of the body and disposed along opposite and parallel sides of the body or, alternatively, along each side of the body.
The IC may be a surface mounted device ("SMD") designed to be mounted directly on the surface of a circuit board, motherboard or within a suitable receiving socket. Alternatively, an IC may be a dual-in-line packaged ("DIP") device intended for mounting with leads passing through the circuit board or within a suitable socket rather than for surface mounting.
Regardless of the nature of the semiconductor device or the manner of mounting, the reliability and functionality of the IC embodied in the device are important considerations for both manufacturers and users alike. A manufacturer, for example, may wish to inspect a production run or lot of semiconductor devices and discard those found to be defective. Additionally, the manufacturer would like to obtain a true and correct assessment of the capabilities of the device such as, for example, the maximum operating speed, which are directly related to the price the manufacturer can charge for the device. A customer, on the other hand, seeks an assurance that the device purchased from the manufacturer will perform according to manufacturer's specifications under real operating conditions.
Both manual and automatic apparatuses have been developed for testing the performance of an IC. Manual testing requires the operator to manually place each device into a test circuit board, conduct the test and then remove the device from the test equipment. By contrast, an automatic testing apparatus, commonly known as a "handler," includes a mechanism for automatically moving the DUT into electrical contact with the testing apparatus. In a typical handler, the device is momentarily brought to rest at a test station where a contactor mounted on a handler interface board (HIB) or motherboard connects to the pins of the IC and establishes a signal path or link between the device and the testing apparatus. To determine whether a device is defective or functional, a series of test signals having a known response is generated by the testing apparatus and delivered by the contactor to the device. The response at some or all of the pins is then measured and compared to the expected response. If the results of the test do not match the predetermined responses, the device is considered to be defective or of an inferior performance grade, and may then be disposed of as appropriate.
Present technology contactors have been designed to be as short as possible so as to increase the bandwidth and reduce the length of the signal path. While such short length contactors work well in the electrical arena, short contactors cause problems in the temperature arena. First, when the contactor is short, the DUT cannot be positioned deep within the test chamber, and, therefore, it is subject to temperature fluctuations caused by the external environment. Second, the short length acts as a heat conduit adversely affecting the temperature of the DUT. Specifically, when being tested at a higher temperature and the DUT is connected to the contactor, the contactor acts as a heat sink and rapidly degrades the temperature of the DUT. Conversely, when the DUT is at a lower temperature, the test chamber and the ambient world are divided only by the thickness of the HIB, which may lead to condensation. It seems axiomatic that, if short contactors have deficiencies, longer contactors would be better. However, simply increasing the length of the contactor can cause other problems.
The testing of integrated circuits frequently requires that the test signal be "fast-rising," that is, a signal which is a very steep, step-like increase in potential. A typical fast-rising signal may be characterized by a voltage change of 1 volt per nanosecond. Such a signal can be represented through Fourier Series analysis as being composed of a multitude of superimposed sine waves have a very high frequency, typically on the order of 300 MHz. The fast-rising signal launched by the test circuitry and carried by the contactors to the device therefore behave in the manner of a high frequency signal. The phrase "high frequency", as used in this document, refers to such fast rising signals having step-like changes in potential.
With such high frequency components in the signal, the inherent inductance of the contactors themselves becomes a problem. Inductive reactance X.sub.L produces distortions and reflections which degrade the quality and accuracy of the test. The inductance L of the contactor is a function of the cross-sectional configuration of the conductors within the contactor and its length. Inductance increases directly with the length and inversely with the cross-sectional width. Because the inductive reactance X.sub.L =2.multidot..pi..multidot.f.multidot.L, for the very high frequencies associated with a fast-rising signal, the inductive reactance associated with even the relatively short contactors in normal use becomes a significant source of distortion and limits the accuracy of measurements.
One possible solution would be to increase the width of the conductors within the contactors. However, the physical constraints of the test environment limit the available dimensions. For example, the conductors must be separated laterally from adjacent conductors which each still maintaining a unique association with one lead on the DUT.
Another possible solution is simply to test each device more slowly to wait for distortions and reflections to die out. With many modem IC's, such as large memory devices, however, the speed of operation of the device itself is so fast that if the testing operation were to extend over a sufficient period of time to allow distortions and echoes induced by the fast-rising testing signal to subside, then the speed rating of the device could not be determined. In short, the testing operation must have a speed on the order of the device function being tested. Thus, the need exists for a contactor that is sufficiently long so as to provide good performance in the temperature arena while not degrading the electrical performance.